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            <h2 class="title" style="clear: both"><a id="dpl_entityjoin"></a>Join Cursors</h2>
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      <p>
                        If you have two or more secondary indexes set for
                        an entity object, then you can retrieve sets of
                        objects based on the intersection of multiple
                        secondary index values. You do this using an
                        <code class="classname">EntityJoin</code>
                        class.
                </p>
      <p>
                        For example, suppose you had an entity class that
                        represented automobiles. In that case, you might
                        be storing information about automobiles such as
                        color, number of doors, fuel mileage,
                        automobile type, number of passengers, make, model, and year,
                        to name just a few.
                </p>
      <p>
                        If you created a secondary index based this
                        information, then you could use an
                        <code class="classname">EntityJoin</code> to return
                        all those objects representing cars with, say, two
                        doors, that were built in 2002, and which are green
                        in color.
                </p>
      <p>
                        To create a join cursor, you:
                </p>
      <div class="orderedlist">
        <ol type="1">
          <li>
            <p>
                                        Open the primary index for the
                                        entity class on which you want to
                                        perform the join.
                                </p>
          </li>
          <li>
            <p>
                                        Open the secondary indexes that you
                                        want to use for the join.
                                </p>
          </li>
          <li>
            <p>
                                        Instantiate an
                                        <code class="classname">EntityJoin</code>
                                        object (you use the primary index
                                        to do this).
                                </p>
          </li>
          <li>
            <p>
                                        Use two or more calls to 
                                        <code class="methodname">EntityJoin.addCondition()</code>
                                        to identify the secondary indexes
                                        and their values that you want to use
                                        for the equality match.
                                </p>
          </li>
          <li>
            <p>
                                        Call
                                        <code class="methodname">EntityJoin.entities()</code>
                                        to obtain a cursor that you can use
                                        to iterate over the join results.
                                </p>
          </li>
        </ol>
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      <p>
                        For example, suppose we had an entity class
                        that included the following features:
                </p>
      <pre class="programlisting">package persist.gettingStarted;

import com.sleepycat.persist.model.Entity;
import com.sleepycat.persist.model.PrimaryKey;
import static com.sleepycat.persist.model.Relationship.*;
import com.sleepycat.persist.model.SecondaryKey;

@Entity
public class Automobiles {

    // Primary key is the vehicle identification number
    @PrimaryKey
    private String vin;

    // Secondary key is the vehicle's make
    @SecondaryKey(relate=MANY_TO_ONE)
    private String make;

    // Secondary key is the vehicle's color
    @SecondaryKey(relate=MANY_TO_ONE)
    private String color;

    ...

    public String getVIN() {
        return vin;
    }

    public String getMake() {
        return make;
    }

    public String getColor() {
        return color;
    }
    
    ... </pre>
      <p>
            Then we could perform an entity join that searches for all the
            red automobiles made by Toyota as follows:
    </p>
      <pre class="programlisting">
PrimaryIndex&lt;String,Automobiles&gt; vin_pidx;
SecondaryIndex&lt;String,String,Automobiles&gt; make_sidx;
SecondaryIndex&lt;String,String,Automobiles&gt; color_sidx;

EntityJoin&lt;String,Automobiles&gt; join = new EntityJoin(vin_pidx);
join.addCondition(make_sidx,"Toyota");
join.addCondition(color_sidx,"Red");

// Now iterate over the results of the join operation
ForwardCursor&lt;Automobiles&gt; join_cursor = join.entities();
try {
    for (Automobiles autoi : join_cursor) {
        // do something with each object "autoi"
    }
// Always make sure the cursor is closed when we are done with it.
} finally {
    join_cursor.close();
} </pre>
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